2492 On new British Entomostraca. 
were females, some of which bore eggs, the few males met 
with being mostly attached to females, the prehensile 
antenna clasping the base of the fureal sete. It is curious 
that in all cases the females so selected were immature and 
showed no sign of developing ova. In one case the female 
was so far from maturity that all the branches of the 
swimming-legs were two-jointed. It is commonly the case 
among Harpacticids and Cyclops that the male should attach 
himself to the female before the last moult, but I think it is 
most unusual for such attachment to take place when at least 
two moults must intervene before copulation can be effective, 
In the same collection were found Mesochra rapiens, Nan- 
nopus palustris, Tachidius littoralis, Poppe, and Heterotanats 
gurneyi, Norman, but, though these are all “ brackish-water ” 
species, a number of freshwater Entomostraca such as Vitocra 
hibernica also occurred, and the plankton at this point in the 
river was that of pure fresh water. Although at the time 
when the collection was made the tide was flowing and nearly 
at high water, the salinity was only ‘09 grms. chlorine per 
litre. At Acle, about 11 miles from Yarmouth, the water is 
usually fresh at all states of the tide, but it is very near the 
upper limit to which salt water penetrates, and no doubt it 
does reach this point fairly often. The locality is therefore 
of some special interest, since it is the meeting-place of salt- 
and freshwater species and has a very mixed fauna. MM. estu- 
art probably belongs to the brackish fauna, and will no doubt 
be found to be common in the lower reaches of the river. 
The genus Mesochra, as defined by Prof, Sars (‘ Crustacea 
of Norway’), differs from Canthocamptus in the reduced 
number of joints in the first antenna, the absence of spines 
on the operculum, and the possession of two well-developed 
joints in the inner branch of legs 2, 38, and 4. Further, the 
swimming-legs of the male are scarcely modified. The 
absence of spines on the operculum is not a constant character, 
since such spines are present in the male of M. rapiens, in 
both sexes of MZ. estuarit, andin M. lybtea, Richard, M. pro- 
wazeki, Daday, and M. deiterst, Rich., all of which seem 
properly to belong to the genus. The species of the genus 
found in Britain are as follows :— 
M. lilljeborgii. 
M. rapiens (Schmeil). 
M. ineonspicua (Scott). 
M. macintoshi, Scott. 
M. parva (T. and A. Scott). 
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